Trilobites: Scientists Made Snails Remember Something That Never Happened to Them

In experiments on Aplysia californica, a sea snail, untrained snails behaved like trained snails after a transfer of molecules from the brains of the trained snails.CreditScience Stock Photography/Science Source

May 15, 2018

Transferring memories from one living thing to another sounds like the plot of an episode of “Black Mirror.” But it may be more realistic than it sounds — at least for snails.

In a paper published Monday in the journal eNeuro, scientists at the University of California-Los Angeles reported that when they transferred molecules from the brain cells of trained snails to untrained snails, the animals behaved as if they remembered the trained snails’ experiences.

David Glanzman, a professor of neurobiology at U.C.L.A. who is an author of the new paper, has been studying Aplysia californica, a sea snail, and its ability to make long-term memories for years. The snails, which are about five inches long, are a useful organism for studying how memories are formed because their neurons are large and relatively easy to work with.

In experiments by Dr. Glanzman and colleagues, when these snails get a little electric shock, they briefly retract their frilly siphons, which they use for expelling waste. A snail that has been shocked before, however, retracts its siphon for much longer than a new snail recruit.

Recently, the scientists realized that even when they interfered with their trained snails’ brain cells in a way that should have removed the memory completely, some vestige remained. They decided to see whether something beyond the brain cells’ connections to each other — namely, RNA — could be hanging on to the memory.

You might remember RNA from high school biology: It is best known for ferrying messages between the genome and the rest of the cell. But scientists have gradually realized that there is more to RNA than playing messenger.

There are some kinds of RNA that, instead of carrying messages, help switch genes on and off. They have been shown to be involved in long-term memory in snails, mice and rats, through their ability to influence chemical tags on DNA. These tags in turn influence whether a gene will be turned on in an organism.

To understand what was happening in their snails, the researchers first extracted all the RNA from the brain cells of trained snails, and injected it into new snails. To their surprise, the new snails kept their siphons wrapped up much longer after a shock, almost as if they’d been trained.

Next, the researchers took the brain cells of trained snails and untrained snails and grew them in the lab. They bathed the untrained neurons in RNA from trained cells, then gave them a shock, and saw that they fired in the same way that trained neurons do. The memory of the trained cells appeared to have been transferred to the untrained ones.

Importantly, when the researchers gave the new snails a drug that keeps chemical tags from being added to DNA, the memory did not transfer. That is in line with other experiments that have suggested that blocking the formation of such tags blocks the formation of long-term memory in snails and some rodents, said Dr. Glanzman. That suggests that what they are seeing is in fact related to memory, and not something else to do with the influx of new RNA.

Earlier reporting on memory research

The First Step Toward a Personal Memory Maker?

Feb. 12, 2018

Swatting at Mosquitoes May Help You Avoid Bites, Even if You Miss

Jan. 25, 2018

Plants Remember You if You Mess With Them Enough

March 28, 2016

The research has echoes of studies from the 1960s involving flatworms. Back then, scientists indulged in a little vicarious cannibalism: They chopped up flatworms trained to respond to light, then fed the remains to other flatworms, to see whether the dead flatworms’ memories would transfer. Oddly enough, it looked like they did. But the results were difficult to replicate. The field moved on.

Dr. Glanzman said that this is the first study since the flatworm work to propose that memories can be transferred in such a way. “It feels like I’m way out on a limb, frankly,” he said.

The team’s findings are a long way still from being applied to people and how our memories form. But Dr. Glanzman hopes others will try to replicate the experiments in other animals, potentially opening the door one day to understanding how RNA and genetic tags on DNA could be involved in memory.